When transmitting a signal between a plurality of semiconductor chips with different power supply voltages, if the signal is transmitted directly through a wire, it can cause damage to the semiconductor chips or a problem in signal transmission due to a voltage difference generated in the DC voltage component of the transmitted signal. Thus, when transmitting a signal between a plurality of semiconductor chips with different power supply voltages, the semiconductor chips are connected via an AC coupling device, so that only an AC signal is transmitted. As the AC coupling device, a capacitor or a transformer can be used.
The transformer is an AC coupling device where a primary coil and a secondary coil are magnetically coupled. In the case of using the transformer as the AC coupling device, by adjusting the winding ratio of the primary coil and the secondary coil of the transformer, a signal (received signal) with an appropriate voltage amplitude is transmitted to the semiconductor chip on the receiving end regardless of the voltage amplitude of a signal (transmission signal) transmitted from the semiconductor chip on the transmitting end. Therefore, by performing communication between the semiconductor chips operating at different power supply voltages through the transformer, there is no need to adjust the voltage amplitude of the transmission signal or the received signal on the semiconductor chip. In the following description, the transformer that is formed on the semiconductor chip is referred to as “on-chip transformer” according to several cases.
Examples of signal transmission techniques using a transformer are disclosed in Patent Literatures 1 to 6 and Non Patent Literature 1.
Patent Literatures 1 and 2 disclose the technique that uses two on-chip transformers and sends out a pulse signal to a first transformer when the value of data changes from a first value to a second value, and sends out the pulse signal to a second transformer when the value of data changes from the second value to the first value.
Patent Literature 3 discloses the structure in which a transformer is formed on another chip placed between a first semiconductor chip and a second semiconductor chip.
Patent Literature 4 discloses the technique that sends out a signal composed of one pulse to an on-chip transformer when the value of data changes from a first value to a second value, and sends out a signal composed of two pulses to the on-chip transformer when the value of data changes from the second value to the first value.
Patent Literature 5 discloses the technique that sends out a continuous pulse signal to an on-chip transformer during a period where the value of data is a first value, and fixes a signal to the on-chip transformer during a period where the value of data is a second value.
Patent Literature 6 discloses the technique that performs signal transmission between a primary circuit and a secondary circuit insulated from each other by using a transformer.
Non Patent Literature 1 discloses the technique that performs signal transmission between a high-voltage power circuit unit and a low-voltage control circuit unit through an on-chip transformer.